Optical information processing apparatus, optical pick-up device and optical recording disc system

ABSTRACT

An optical pick-up device includes a laser diode, an objective lens for focusing a light beam emitted from the laser diode on an optical disc, an optical detector for receiving a reflected beam from the optical disc, a beam splitter for causing the light beam emitted from the laser diode and a reflected beam to pass therethrough or reflect, a front monitor for receiving the light beam emitted from the laser diode, and a front monitor light-guiding plate for guiding a part of the light beam emitted from the laser diode to the front monitor. The front monitor light-guiding plate is arranged between the laser diode and the objective lens and has a region having a predetermined shape for causing the part of the light incident thereon to change a traveling direction thereof by refraction and then reach the front monitor.

INCORPORATION BY REFERENCE

The present application claims priority from Japanese application JP2004-325814 filed on Nov. 10, 2004, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

The present invention relates to a technical field concerning opticalinformation processing.

In recent years, optical disc drives capable of recording information onand reproducing the information from CD-R/RW (CompactDisc-Recordable/Rewritable), DVD-R/RW (Digital VersatileDisc-Recordable/Rewritable), or the like have become widely spread. Inthe optical disc drive, in order to record the information, a light beamis irradiated onto an optical disc by an optical pick-up devicecontained in the optical disc drive. Then, in order to read theinformation, the light beam reflected from the optical disc is detectedby the optical pick-up device.

In order to perform stable recording and reproduction processing duringthe recording and reproduction of the information by the optical pick-updevice, it is necessary to accurately control the light amount of thelight beam irradiated onto the optical disc. For this reason, theoptical pick-up device has a unit for detecting the light amount of thelight beam emitted from a laser diode. By feedbacking the detected lightamount to the laser diode, the light amount of the light beam irradiatedonto the optical disc is accurately controlled.

In order to detect the light amount of the light beam emitted from thelaser diode, it is a common practice to provide a light receptionelement that receives a part of the light beam emitted forward from thelaser diode. Herein, the light reception element that receives the lightbeam emitted forward from the chip of the laser diode will be referredto as a “front monitor”.

Various units for guiding the light beam from the laser diode to thefront monitor are known.

Among these, an optical pick-up device disclosed in FIG. 1 ofJP-A-2001-184709, for example, has a configuration in which a light beamis emitted from a laser diode, and a part of the emitted light beamoutside the effective diameter of an objective lens is detected by afront monitor.

In this configuration, the light beam outside the effective diameter ofthe objective lens is monitored. Thus, it is possible to avoid a problemthat a light amount detected by the front monitor is greatly varied.This problem occurs due to interference between the light beam emittedfrom the laser diode and a light beam reflected from the optical disc onthe detection surface of the front monitor.

An optical pick-up device disclosed in FIG. 1 of JP-A-2003-77170, forexample, has a configuration in which a diffraction element is arrangedbetween an objective lens and a laser diode, so that the light amount ofthe light beam outside the effective diameter of an objective lens isled more to the front monitor.

SUMMARY OF THE INVENTION

In recent years, in order to support high-speed recording in CD and DVD,it is necessary to mount the high-power laser diode in the opticalpick-up device. When the optical output of the high-power laser diode isincreased, the center of the optical axis of the laser diode may beinclined. When the center of the optical axis is inclined in the opticalpick-up device as disclosed in JP-A-2001-184709, which detects a part ofthe light beam outside the effective diameter of the objective lens bythe front monitor, the amount of light detected by the front monitorwill be greatly varied, for example, even with the amount of lightirradiated onto the optical disc practically unchanged. The amount ofthe light thus cannot be monitored accurately.

On the other hand, in the configuration that uses the diffractionelement as disclosed in JP-A-2003-77170, in addition to a light beamhaving a predetermined angle, a light beam having a diffraction angleother than the predetermined diffraction angle is also generated by thediffraction element. This light beam may become a stray light, and mayenter into a detector or the like for detecting an information signal,thereby hindering high-accuracy signal reproduction. For this reason,countermeasures against the stray light are required for each of theoptical pick-up devices that have been mass produced. Improvement in theyield of the optical pick-up devices is thereby hindered.

An object of the present invention is therefore to downsize an opticalinformation processing apparatus or reduce the circuit size of theoptical information processing apparatus. The above-mentioned object isachieved by the invention defined in claims, so that downsizing theoptical information processing apparatus or reduction in the circuitsize of the optical information processing apparatus can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, objects and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawing wherein:

FIG. 1 is a diagram showing a configuration of an optical system of anoptical pick-up device in a first embodiment;

FIG. 2 is a schematic diagram showing a configuration of a front monitorlight-guiding plate in the first embodiment;

FIG. 3 is a schematic diagram showing a configuration of a front monitorlight-guiding plate in a second embodiment;

FIG. 4 is a diagram showing a configuration of an optical system of anoptical pick-up device in a third embodiment;

FIG. 5 is a schematic diagram showing a configuration of a front monitorlight-guiding plate in the third embodiment;

FIG. 6 is a diagram showing a configuration of an optical system of anoptical pick-up device in a fourth embodiment;

FIG. 7 is a schematic diagram showing a configuration of a front monitorlight-guiding plate in the fourth embodiment;

FIG. 8 a diagram showing configurations of optical systems of an opticalpick-up device in a fifth embodiment;

FIG. 9 is a schematic block diagram showing a configuration of anoptical recording disc system in a sixth embodiment; and

FIG. 10 shows a state in which a light beam changes its travelingdirection in a region of a front monitor light-guiding plate of theoptical system.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A best mode for carrying out the present invention will be described inthe order of first through sixth embodiments.

In the first embodiment, a description will be directed to an opticalpick-up device that supports an optical disc drive capable of performingrecording on and reproduction from a DVD.

FIG. 1 is a diagram showing an optically devised configuration includingan optical pick-up device 100. A light beam is emitted from a laserdiode 1 as diverged beams. In order to perform information recording onor information reproduction from a DVD optical disc, it is a commonpractice to employ a semiconductor laser with a wavelength ofapproximately 660 nm. As the laser diode 1 as well, the semiconductorlaser that emits a light beam with a wavelength of approximately 660 nmis assumed. It is also assumed that a laser chip active layer in thelaser diode 1 is parallel to a plane formed by x and y axes in FIG. 1.Further, a light path indicated by cross hatching in FIG. 1 represents alight beam 2, while a light path indicated by a chain line represents alight beam 3.

First, the light beam 2 will be described. The light beam 2 emitted fromthe laser diode 1 enters a front monitor light-guiding plate 4, which isa transparent substrate. In the front monitor light-guiding plate 4, aregion 5 with light incident and emergent surfaces thereof set atpredetermined angles, respectively, is formed. The light beam 2, whichhas entered into the region 5 in the front monitor light-guiding plate4, exits the front monitor light-guiding plate 4 at a predeterminedangle by refraction. The light beam 2 which has exited the front monitorlight-guiding plate 4 is reflected at a beam splitter 6 once, and thenenters into a front monitor 7.

In the optical disc drive, when a signal is recorded on the opticaldisc, a predetermined amount of light is irradiated onto the opticaldisc, as described before. Accordingly, it is necessary to accuratelycontrol the amount of light emitted from the laser diode. The frontmonitor 7 is thus mounted to detect a change in the amount of the lightfrom the laser diode 1 and control the amount of the light emitted fromthe laser diode 1. The output signal of the front monitor 7 is fed backto a driving circuit (not shown) for the laser diode 1. The outputsignal thus can control the amount of the light emitted from the laserdiode 1, so that a desired amount of light can be irradiated onto theoptical disc.

Next, the light beam 3 will be described. The light beam 3 emitted fromthe laser diode 1 enters the front monitor light-guiding plate 4. In aregion different from the region 5 in the front monitor light-guidingplate 4, grating grooves are formed. The light beam 3 is branched intothree beams through the grating grooves, for use in detecting a trackingerror signal (hereinafter referred to as a TES) for the optical discthrough a differential push-pull method (hereinafter referred to as aDPP method). Since the DPP method is a very common method of detectingthe TES, its description will be omitted. The light beam 3 that haspassed through the front monitor light-guiding plate 4 reflects from thebeam splitter 6. Then, the light beam 3 is guided to a collimating lens8, through which the light beam 3 is converted into generally parallellight beams. The generally parallel light beams converted from the lightbeam 3 exit the collimating lens 8, reflect from a reflection mirror 9in the positive direction of a z axis shown in FIG. 1, and are focusedon the optical disc (not shown) through an objective lens 11 mounted onan actuator 10.

The light beam 3 is reflected from the optical disc and reaches anoptical detector 13 through the objective lens 11, reflection mirror 9,collimating lens 8, beam splitter 6, and a detecting lens 12. When thelight beam 3 passes through the beam splitter 6, the light beam 3 isgiven predetermined astigmatism and is used for detecting a focusingerror signal (hereinafter referred to as an FES) for the optical discthrough an Astigmatic Detection method. Since the Astigmatic Detectionmethod is a very common method of detecting the FES, its descriptionwill be omitted. The detecting lens 12 functions to turn the directionof the astigmatism in a predetermined direction and also functions todetermine the size of a light spot on the optical detector 13. The lightbeam 3 guided to the optical detector 13 is used for detection of aninformation signal recorded on the optical disc and detection ofposition control signals such as the TES and the FES for a light spotfocused on the optical disc.

FIG. 2 is a schematic diagram showing a configuration of the frontmonitor light-guiding plate 4. The front monitor light-guiding plate 4will be described in detail with reference to FIG. 2. A drawing on theleft shows the front monitor light-guiding plate 4 seen from a point ain FIG. 1, while a drawing on the right shows the front monitorlight-guiding plate 4 seen from a point b in FIG. 1.

In the front monitor light-guiding plate 4, the region 5 is formed. Theregion 5 has the light incident and emergent set at the predeterminedangles. The light incident is set at the predetermined angles withrespect to the y and z axes, respectively. The light emergent surface isalso set at the predetermined angles with respect to the y and z axes,respectively. By setting the surface shapes of the light incident andemergent surfaces the region 5 at the predetermined angles as describedabove, the light beam 2 that has passed through the region 5 of thefront monitor light-guiding plate 4 is guided to the front monitor 7 byrefraction.

A circle 14 in the right drawing indicates a region in the front monitorlight-guiding plate 4 illuminated by the light beam 3 within theeffective diameter of the objective lens 11. When predeterminedpositional information on the optical disc is recorded or reproduced,the objective lens 11 is moved in the radial direction of the opticaldisc, for use. For this reason, the region of the front monitorlight-guiding plate 4 illuminated by the light beam, such as a circle 15or a circle 16 indicated by a broken line is wide in the positive andnegative directions of the y axis. In optical recording disc systems inrecent years, in order to increase the speed of recording, not only thepower of the laser diode but also the optical efficiency with which alight beam is guided to the optical disc must be increased. For thispurpose, the region 5 of the front monitor light-guiding plate 4 isarranged outside the region illuminated by the light beam 3 within theeffective diameter of the objective lens 11. Since the light beam 2outside the effective diameter of the objective lens is used asdescribed above, the optical efficiency with which the light beam isguided to the optical disc will not be reduced.

Further, the light beam emitted from the laser diode generally has anelliptical intensity distribution in a longitudinal direction orthogonalto the laser chip active layer of the laser diode, an ellipticalintensity distribution 18 as shown in a dotted line in the right drawingis obtained. For this reason, the region 5 of the front monitorlight-guiding plate 4 is so arranged as to cross a straight line (a line17 in the drawing) passing through the center of the light beam 3 andperpendicular to the laser chip active layer of the laser diode. Withthis arrangement, the amount of light that reaches the front monitor 7is increased, so that a signal having a good SN (signal to noise ratio)can be obtained.

The front monitor light-guiding plate 4 is arranged in the light pathbetween the laser diode 1 and the objective lens 11, and the gratinggrooves are formed in the region of the front monitor light-guidingplate 4 illuminated by the light beam 3 within the effective diameter ofthe objective lens 11. With this arrangement, the front monitorlight-guiding plate 4 also has a function comparable to that of anordinary diffraction grating. Thus, without arranging the front monitorlight-guiding plate and the diffraction grating separately, as inJP-A-2001-184709, two types of functions can be incorporated into onlyone component. Downsizing can be thereby achieved, and low cost due toreduction of an assembly time as well as a decrease in the number ofcomponents can also be achieved.

Further, in this embodiment, the light beam is guided to the frontmonitor by refraction. Thus, compared with a configuration as disclosedin JP-A-2003-77170, in which the light beam is guided to the frontmonitor by diffraction, measures against a stray light are not required.

Still further, by setting the light incident and emergent surfaces ofthe region 5 of the front monitor light-guiding plate 4 at thepredetermined angles, greater mounting latitude in the arrangement ofthe front monitor 7 is achieved.

In the optical recording disc system, higher reflectivity andtransmittivity of the beam splitter 6 are required. The higherreflectivity is required for increasing the power for irradiating alight beam onto the optical disc. The higher transmittivity is requiredfor improving the SN of the optical detector. A special film is formedon the surface of the beam splitter 6 so that the beam splitter 6 hasspecial reflection and transmission characteristics. Preparation of sucha special film, however, is very difficult, and depending on the film,the reflection and transmission characteristics would greatly vary. Forthis reason, when the reflectivity of the beam splitter 6 is reduced ina conventional optical recording disc system, the amount of light on theoptical disc is reduced though the amount of light on the front monitorremains unchanged. Thus, in the present invention, the front monitor 7is arranged in a position that is more ahead in the traveling directionof the light beam 2 than the beam splitter 6. With this arrangement, theamount of the light detected by the front monitor will not depend on thereflection and transmission characteristics of the beam splitter 6.

FIG. 10 shows a state in which the light beam changes its travelingdirection in the region 5 of the front monitor light-guiding plate 4 byrefraction. The light beam enters into the region 5 from a point A inFIG. 10. The light incident surface is arranged inclined by apredetermined angle θA with respect to the light beam. The light beampasses through the region 5, being inclined by an angle θa differentfrom the angle θA in accordance with the Snell's law. The light emergentsurface is arranged inclined by an angle θb with respect to the lightbeam that enters the light emergent surface. The light beam exits theregion 5, being inclined by an angle θB different from the angel θb inaccordance with the Snell's law. The light beam that has entered intothe region 5 from the point A exits the region 5, being inclined by theangle different from the original angle. By setting the light incidentand emergent surfaces arbitrarily, the light beam inclined by anarbitrary angle can be obtained. The present invention utilizes such arefraction phenomenon and guides the light beam outside the effectivediameter of the objective lens to the front monitor 7 through the frontmonitor light-guiding plate 4.

In the first embodiment, a description was directed to the opticalpick-up device that supports the optical disc drive that can performrecording on and reproduction from the DVD. The optical pick-up devicethat supports the optical disc drive capable of performing recording onand reproduction from media such as a CD, BD (Blu-ray Disc), and HD-DVD(High Definition-DVDs) can also be used. The optical pick-up device canbe used as the optical pick-up device for the CD, BD, HD-DVD. Theoptical pickup device can be of course used as the compatible opticalpick-up device for light beams of a plurality of wavelengths, such as atwo-wavelength compatible optical pickup device for the CD and the DVDor a three-wavelength compatible optical pickup device for the BD, DVD,and CD.

In the second embodiment, a description will be directed to an opticalpick-up device that supports the optical disc drive capable ofperforming recording on and reproduction from the DVD. The opticalpick-up device in the second embodiment is different from the opticalpick-up device 100 in the first embodiment in the structure of the frontmonitor light-guiding plate 4. Since the optical pick-up device in thesecond embodiment is the same as the optical pick-up device 100 exceptfor the front monitor light-guiding plate 4, a detailed description ofthe optical pick-up device will be omitted.

FIG. 3 is a schematic diagram showing the front monitor light-guidingplate 4 in the second embodiment. The front monitor light-guiding plate4 in the second embodiment is different from the front monitorlight-guiding plate 4 in the first embodiment in that a region 20 isformed. The region 20 has the light incident and emergent surfaces setat predetermined angles. The light incident surface is set at thepredetermined angles with respect to the y and z axes, respectively. Thelight emergent surface is also set at the predetermined angles withrespect to the y and z axes, respectively. The angles at which the lightincident and emergent surfaces are set in the area 20 are different fromthose in the region 5. By setting the surface shapes of the lightincident and emergent surfaces of the region 20 at the predeterminedangles, the light beam 2 that has passed through the region 20 of thefront monitor light-guiding plate 4, is also guided to the front monitor7 by refraction.

In the second embodiment, the light beam emitted from the laser diode 1is guided to the front monitor 7 from the two regions 5 and 20 in thefront monitor light-guiding plate 4. Thus, the amount of light thatreaches the front monitor 7 is doubled compared with that in the firstembodiment.

Further, like the region 5, the region 20 of the front monitorlight-guiding plate 4 is arranged outside the region illuminated by thelight beam 3 within the effective diameter of the objective lens. Sincethe region 20 also uses the light beam outside the effective diameter ofthe objective lens, the optical efficiency with which the light beam isguided to the optical disc will not be reduced.

Further, the light beam of the laser diode has generally the ellipticalintensity distribution 18 in the longitudinal direction orthogonal tothe laser chip active layer. For this reason, the region 20 of the frontmonitor light-guiding plate 4 is also so arranged as to cross thestraight line (the line 17 in the drawing) passing through the center ofthe light beam 3 and perpendicular to the laser chip active layer of thelaser diode. With this arrangement, the amount of the light that reachesthe front monitor 7 is increased, so that a signal with a good SN(signal to noise ratio) can be obtained.

As described before, in recent years, when the optical output of thehigh-power laser diode for supporting high-speed recording on the CDsand the DVDs is increased, the center of the optical axis of the laserdiode may be inclined. When the center of the optical axis is inclinedin the optical pick-up device as disclosed in JP-A-2001-184709, whichdetects a part of the emitted light beam outside the effective diameterof the objective lens by the front monitor, the amount of light detectedby the front monitor will be greatly varied, though the amount of lightirradiated onto the optical disc remains unchanged. The amount of thelight thus cannot be detected accurately. This problem arises for thefollowing reason: A light beam irradiated onto the optical disc throughthe objective lens has an intensity peak in the center of the opticalaxis of the light beam. Thus, even if the optical axis is inclined to acertain extent within the effective diameter of the objective lens, achange in power emitted to the optical disc is not great. However, thelight beam guided to the front monitor uses the part of the emittedlight beam outside the effective diameter of the objective lens.Accordingly, when the center of the optical axis is inclined, a changein the position of the intensity distribution of the light beam willdirectly be reflected on the amount of the light detected by the frontmonitor. Accordingly, the amount of the light detected by the frontmonitor will be greatly varied.

For this reason, in the second embodiment, the region 20 of the frontmonitor light-guiding plate 4 is arranged opposite to the region 5 withrespect to a straight line (a line 21 in the drawing) parallel to thelaser chip active layer in the laser diode 1. When the regions 5 and 20are arranged as described above, and when the center of the optical axisis inclined and the amount of light that reaches the front monitor 7from the region 5 is greatly reduced, the amount of light that reachesthe front monitor 7 from the region 20 is greatly increased. The amountof the light detected by the front monitor 7 can be thereby made to bescarcely changed. In other words, a change caused by inclination of theoptical axis can be limited to be a small one.

In the third embodiment, a description will be directed to an opticalpick-up device that supports the optical disc drive capable ofperforming recording on and reproduction from the DVDs.

FIG. 4 is a diagram showing an optical system configuration of anoptical pick-up device 101 in the third embodiment. The optical pick-updevice 101 in the third embodiment is different from the optical pick-updevice 100 in the first embodiment in that all of optical components arerotated by 45 degrees around the z axis with respect to the center ofthe objective lens.

First, the optical system of the optical pick-up device 101 will bedescribed. A light beam is emitted from a laser diode 1 as divergedlights. As in the case of the optical pick-up device 100, thesemiconductor laser that emits the light beam with a wavelength ofapproximately 660 nm is assumed to be used as the laser diode 1. It isalso assumed that the laser chip active layer in the laser diode 1 isparallel to a plane obtained by rotating the plane formed by x and yaxes in FIG. 4 by 45 degrees counterclockwise with respect to the xaxis. Further, a light path indicated by cross hatching in FIG. 4represents the light beam 2, while a light path indicated by a chainline represents the light beam 3.

First, the light beam 2 will be described. The light beam 2 emitted fromthe laser diode 1 enters into front monitor light-guiding plate 4, whichis the transparent substrate. In the front monitor light-guiding plate4, the region 5 is formed. The region 5 has the light incident andemergent surfaces set at predetermined angles, respectively. The lightbeam 2, which has entered into the region 5 in the front monitorlight-guiding plate 4, exits the front monitor light-guiding plate 4 ata predetermined angle by refraction. The light beam 2 which has exitedthe front monitor light-guiding plate 4 reflects from the beam splitter6 once, and then enters the front monitor 7.

Since all of the optical components are rotated around the z axis withrespect to the center of the objective lens, the configuration of thefront monitor light-guiding plate 4 of the optical pick-up device 101becomes different from the configuration of the front monitorlight-guiding plate 4 of the optical pick-up device 100. The frontmonitor light-guiding plate 4 in this embodiment will be described laterin detail using FIG. 5.

Next, the light beam 3 will be described. The light beam 3 emitted fromthe laser diode 1 enters the front monitor light-guiding plate 4. In aregion different from the region 5 in the front monitor light-guidingplate 4, the grating grooves are formed. The light beam 3 is branchedinto three beams through the grating grooves, for use for detecting theTES for an optical disc through the DPP method. The light beam 3 thathas passed through the front monitor light-guiding plate 4 reflects fromthe beam splitter 6. Then, the light beam 3 is guided to the collimatinglens 8, through which the light beam 3 is converted into generallyparallel light beams. The generally parallel light beams converted fromthe light beam 3, which have exited the collimating lens 8, reflect fromthe reflection mirror 9 in the positive direction of the z axis shown inFIG. 4, and are focused on the optical disc (not shown) through theobjective lens 11 mounted on the actuator 10.

The light beam 3 is reflected from the optical lens and reaches theoptical detector 13 through the objective lens 11, reflection mirror 9,collimating lens 8, and beam splitter 6. When the light beam 3 passesthrough the beam splitter 6, the light beam 3 is given predeterminedastigmatism and is used for detecting the FES for the optical disc usingthe Astigmatic Detection method. In the optical pick-up device 101, theoverall optical system is inclined by 45 degrees around the z axis, andthe laser chip active layer in the laser diode 1 is made parallel to theplane obtained by rotating the plane formed by the x and y axes in FIG.4 by 45 degrees counterclockwise with respect to the x axis. Thedetecting lens 12 can be thereby eliminated. The light beam 2 guided tothe optical detector 13 is used for detection of an information signalrecorded on the optical disc and detection of the position controlsignals such as the TES and the FES for a light spot converged on theoptical disc.

FIG. 5 is a schematic diagram showing a configuration of the frontmonitor light-guiding plate 4 in the third embodiment. Using thisdrawing, the front monitor light-guiding plate 4 will be described indetail. FIG. 5 shows the front monitor light-guiding plate 4 seen from apoint b in FIG. 4. The front monitor light-guiding plate 4 in the thirdembodiment is different from the front monitor light-guiding plate 4 inthe first embodiment in FIG. 2 in that the center of the light beam onthe front monitor light-guiding plate 4 is inclined by 45 degreescounterclockwise with respect to the x axis. Further, the laser chipactive layer in the laser diode 1 is made parallel to the plane obtainedby rotating the plane formed by the x and y axes in FIG. 5 by 45 degreescounterclockwise with respect to the x axis. Thus, the ellipticalintensity distribution in the longitudinal direction orthogonal to thelaser chip active layer becomes the elliptical intensity distribution 18as indicated by a dotted line in FIG. 5. The region 5 of the frontmonitor light-guiding plate 4 is arranged so as to cross the straightline (the line 17 in FIG. 5) passing through the center of the lightbeam 3 and perpendicular to the laser chip active layer of the laserdiode. Thus, the center of the light beam on the front monitorlight-guiding plate 4 in the third embodiment is inclined by 45 degreescounterclockwise with respect to the x axis. With this arrangement, theamount of light that reaches the front monitor 7 is increased, so that asignal with a good SN (signal to noise ratio) can be obtained.

The angles at which the light incident and emergent surfaces the region5 are set are of course different from those in FIG. 2, and the lightincident and emergent surfaces are set at desired angles so that thelight beam reaches the front monitor 7.

As the front monitor light-guiding plate 4 of the optical pick-up device101, the front monitor light-guiding plate 4 shown in FIG. 3 can also beused. In this case, by inclining the center of the light beam on thefront monitor light-guiding plate 4 in FIG. 3 by 45 degreescounterclockwise with respect to the x axis, the same effect as thatdescribed in the second embodiment can be obtained.

When the optical recording disc system is mounted in personal computersof a notebook type for mobile use, which have become popular in recentyears, the thinner optical recording disc system is preferable due toconvenience for portability. When the optical recording disc system ismounted in the notebook type personal computer, by inclining the frontmonitor light-guiding plate 4 in an optical axis direction as shown inFIG. 5, the thickness of the optical components therein can also bereduced in the thickness direction of the optical pick-up device.

In the fourth embodiment, a description will be directed to an opticalpick-up device that supports an optical disc drive that can performrecording on and reproduction from the DVD and CD.

FIG. 6 is a diagram showing a configuration of an optical system of anoptical pick-up device 102. The optical pick-up device 102 in the fourthembodiment is different from the optical pick-up device 100 in the firstembodiment in that a two-wavelength multi laser diode 30 is mounted andthe configuration of the front monitor light-guiding plate 4 isdifferent. The two-wavelength multi-laser diode is constituted byforming two different laser chips in one laser diode.

It is a common practice to use the semiconductor laser with a wavelengthof approximately 660 nm to perform information recording on orinformation reproduction from DVD optical discs. It is also a commonpractice to use a semiconductor laser with a wavelength of 780 nm toperform information recording on or information reproduction from CDoptical discs. For this reason, it is assumed that a light beam for aDVD, or a DVD light beam with a wavelength of 660 nm is emitted from thetwo-wavelength multi-laser diode when recording on or reproduction fromthe DVD optical disc is performed. It is also assumed that a light beamfor a CD or a CD light beam with a wavelength of 780 nm is emitted fromthe two-wavelength multi-laser diode when recording on or reproductionfrom the CD optical disc is performed. Further, the laser chip activelayer in the laser diode 30 is assumed to be parallel to a plane formedby x and y axes in FIG. 6. Each of the CD and DVD light beams emittedfrom the two-wavelength multi-laser diode passes through the same lightpath as that in the first embodiment. Thus, a description of the detailsof them will be omitted.

Since the DVD light beam and the CD light beam emitted from the laserdiode 30 are different in wavelength, the angles of refraction of theDVD and CD light beams that have entered into the region 5 in the frontmonitor light-guiding plate 4 are slightly different. Accordingly,between the DVD light beam and the CD light beam, the angles set for thelight incident and emergent surfaces of the region 5 in which the amountof light becomes the largest on the front monitor 7 will becomedifferent.

FIG. 7 shows the configuration of the front monitor light-guiding plate4 in the fourth embodiment. The front monitor light-guiding plate 4 inthis embodiment is different from the front monitor light-guiding plate4 in FIG. 3 in that the configurations of the regions 5 and 20 aredifferent. The angles of the light incident and emergent surfaces ofeach of regions 31 a and 32 a are set so that the light amount of theDVD light beam becomes the largest on the front monitor 7, while theangles of the light incident and emergent surfaces of each of regions 31b and 32 b are set so that the light amount of the CD light beam becomesthe largest on the front monitor 7. Through the use of the front monitorlight-guiding plate 4 having the configuration shown in FIG. 7, theoptimum light amounts for the DVD and the CD can be respectively led tothe front monitor 7. Consequently, high accuracy detection of therespective light amounts on the DVD and CD optical discs becomespossible.

Alternatively, even if the light incident and emergent surfaces of theregion 5 are set at optimum angles for the DVD and the light incidentand emergent surfaces of the region 20 are set at optimum angles for theCD in the configuration of the front monitor light-guiding plate 4 shownin FIG. 3, high accuracy detection of the respective light amounts onthe DVD and CD optical discs becomes possible.

Alternatively, when the DVD and CD light beams having differentwavelengths are guided to the front monitor 7 through the front monitorlight-guiding plate 4 having the configuration in FIG. 2, the lightincident and emergent surfaces of the region 5 may be set at anglesintermediate between the optimum angles for the DVD and the CD.

In the fifth embodiment, a description will be directed to an opticalpick-up device that supports the optical disc drive that can performrecording on and reproduction from the DVDs and the CDs.

FIG. 8 is a diagram schematically showing configurations of DVD and CDoptical systems of an optical pick-up device 103.

First, the DVD optical system will be described. A DVD light beam isemitted from a DVD laser diode 40 as diverged lights. The laser diode 40is also assumed to be the semiconductor laser that emits the light beamhaving a wavelength of approximately 660 nm so as to perform informationrecording on or information reproduction from a DVD. A laser chip activelayer in the DVD laser diode 40 is assumed to be parallel to a planeobtained by inclining a plane formed by x and y axes in FIG. 8 by 45degrees counterclockwise with respect to the optical axis of the DVDlight beam.

The DVD light beam emitted from the DVD laser diode 40 enters a frontmonitor light-guiding plate 42. Since the laser chip active layer isinclined with respect to the optical axis, the DVD front monitorlight-guiding plate is assumed to have a shape as shown in FIG. 5. In aregion different from the region 5, the grating grooves are formed. TheDVD light beam is branched into three beams through the grating grooves,for use for detecting the TES for the optical disc through the DPPmethod. The branched light beams of the DVD light beam that have passedthrough the region 5 of the DVD front monitor light-guiding plate 42reflect from beam splitters 43 and 44, respectively, and proceeds to afront monitor 45 arranged below a reflection mirror (in the negativedirection of the z axis in FIG. 8). An output signal indicating theamount of light detected by the front monitor 45 is fed back to adriving circuit (not shown) for the laser diode 40, for use forcontrolling the amount of light emitted from the laser diode 40 andirradiating the optical disc with a desired amount of light.

The DVD light beam that has passed through the region of the DVD frontmonitor light-guiding plate 42 with the grating grooves formed thereinreflects from the beam splitters 43 and 44 and the reflection mirror 46,and then guided to a collimating lens 47, for conversion into generallyparallel light beams. The generally parallel light beams converted fromthe DVD light beam that have exited the collimating lens 47 are focusedon the optical disc (not shown) through an objective lens 48 mounted onan actuator (not shown).

The focused DVD light beam is then reflected from the optical disc, andreaches an optical detector 49 through the objective lens 48,collimating lens 47, reflection mirror 46, beam splitter 44, and beamsplitter 43. When the DVD light beam passes through the beam splitter43, the DVD light beam is given predetermined astigmatism and is usedfor detecting the FES for the optical disc through the AstigmaticDetection method. In the optical pick-up device 101, the overall opticalsystem is inclined by 45 degrees around a z axis, and the laser chipactive layer in the laser diode 40 is made parallel to the planeobtained by rotating the plane formed by the x and y axes in FIG. 8 by45 degrees counterclockwise with respect to the optical axis, thedetecting lens can be eliminated. The DVD light beam guided to theoptical detector 49 is used for detection of an information signalrecorded on the optical disc and detection of the position controlsignals such as the TES and the FES for a light spot converged on theoptical disc.

Next, the CD optical system will be described. A CD light beam isemitted from a DVD laser diode 40 as diverged lights. A CD laser diode50 is also assumed to be the semiconductor laser that emits the lightbeam having a wavelength of approximately 780 nm so as to performinformation recording on or information reproduction from a CD. A laserchip active layer in the CD laser diode 50 is assumed to be parallel toa plane obtained by inclining the plane formed by the x and y axes inFIG. 8 by 45 degrees counterclockwise with respect to the optical axisof the CD beam.

The CD light beam emitted from the CD laser diode 50 enters a correctinglens 51. Since the optimum optical magnification factors of the DVD andthe CD are different in general, the correction lens 51 is disposed inthe CD optical system, for conversion of the substantial focal distanceof the collimating lens by a combined use with the collimating lens 47.The optical magnification factor is herein defined to be the ratio ofthe focal distance of the collimating lens to the focal distance of theobjective lens. The CD light beam that has passed through the correctinglens 51 enters a CD front monitor light-guiding plate 52. Since thelaser chip active layer is inclined with respect to the optical axis,the CD front monitor light-guiding plate 52 is assumed to have the shapeas shown in FIG. 5. In the region different from the region 5, thegrating grooves are formed. The CD light beam is branched into threebeams through the grating grooves, for use for detecting the TES for theoptical disc through the DPP method. The three beams branched from theCD light beam that have passed through the region 5 of the DVD frontmonitor light-guiding plate 52 pass through the beam splitter 44, andproceeds to the front monitor 45 arranged below the reflection mirror(in the negative direction of the z axis in FIG. 8). An output signalindicating the amount of light detected by the front monitor 45 is fedback to a driving circuit (not shown) for the laser diode 50, for usefor controlling the amount of light emitted from the laser diode 50 andirradiating the optical disc with a desired amount of light.

The CD light beam that has passed through the region of the CD frontmonitor light-guiding plate 52 with the grating grooves formed thereinpasses through the beam splitter 44. When a diverged light have passedthrough an inclined parallel plate such as the beam splitter 44,astigmatism and coma aberration occur. The light incident surface of thecorrecting lens 52 is set to be cylindrical so that the astigmatism andthe coma aberration that occur when the CD light beam passes through thebeam splitter 44 are removed. After the branched light beams of the CDlight beam have passed through the beam splitter 44, the branched lightbeams reflect from the reflection mirror 46, and then guided to thecollimating lens 47, for conversion into generally parallel light beams.The generally parallel light beams emitted from the collimating lens 47are focused on the optical disc (not shown) through the objective lens48 mounted on the actuator (not shown).

The focused CD light beam is reflected from the optical disc, andreaches the optical detector 49 through the objective lens 48,collimating lens 47, reflection mirror 46, beam splitter 44, and beamsplitter 43. When the CD light beam passes through the beam splitter 43,the CD light beam is given predetermined astigmatism and is used fordetecting the FES for the optical disc through the Astigmatic Detectionmethod, like the DVD light beam. The CD light beam guided to the opticaldetector 49 is used for detection of an information signal recorded onthe optical disc and detection of the position control signals such asthe TES and the FES for a light spot converged on the optical disc.

As described above, different front monitor light-guiding plates may bedisposed for the DVD optical system and the CD optical system, as inFIG. 8. By disposing the different front monitor light-guiding plates,the light incident and emergent surfaces of the regions 5 of the frontmonitor light-guiding plates can be set at optimum angles, respectively.Thus, it becomes possible to control the powers of the DVD optical discand the CD optical disc with higher accuracy.

In the sixth embodiment, an optical recording disc system including theoptical pick-up device described before will be described.

FIG. 9 is a schematic block diagram of an optical recording disc systemfor recording and reproduction, including the optical pick-up device100. Signals detected by the optical pick-up device 100 are transmittedto a servo signal generation circuit 71, a front monitor circuit 72, andinformation signal reproduction circuit 75 in a signal processingcircuit. In the servo signal generation circuit 71, the FES and the TESsuitable for each optical disc are generated from these detectedsignals. Based on the TES and the FES, the actuator for the objectivelens in the optical pick-up device 100 is driven through an actuatordriving circuit 70 to perform position control of the objective lens.The front monitor circuit 72 detects a light amount monitoring signalfor the laser diode from the detection signal of the front monitor, andbased on this signal, a laser diode control circuit 73 is driven toperform control over the amount of light on an optical disc 150 withaccuracy. In the information signal reproduction circuit 75, aninformation signal recorded on the optical disc 150 is reproduced fromthe detection signals, and the reproduced information signal is outputto an information signal output terminal 79.

When recording information is input to a recording information inputterminal 80, the recording information is converted to a recordingsignal for driving a predetermined laser by a recording informationsignal conversion circuit 76. This laser driving record signal istransmitted to a control circuit 78 to drive the laser diode controlcircuit 73, thereby performing light amount control over the laserdiode. Then, the recording signal is recorded on the optical disc 150.An access control circuit 74 and a spindle motor driving circuit 77 areconnected to this control circuit 78, so that position control over theaccess direction of the optical pick-up device 100 and rotation controlover a spindle motor 81 for the optical disc 150 are performed.

In this sixth embodiment, a description was directed to the opticalpick-up device 100 for use in the DVD optical recording disc systemalone. The optical recording disc system in the sixth embodiment,however, can also be used for any optical pick-up device that supportsan optical disc such as the CD, a BD, or a HD-DVD.

In this sixth embodiment, the description was directed to the opticalpick-up device 100 for use in the DVD optical recording disc systemalone. In the optical recording disc system in the sixth embodiment,however, an optical pick-up device that supports a plurality of opticaldiscs, such as an optical pick-up device for performing recording onboth of the DVD and the CD or a BD/DVD/CD compatible optical pick-updevice for performing recording, can also be used.

In the first through sixth embodiments, the grating grooves were formedin the region of the front monitor light-guiding plate except for theregion through which the light beam is guided to the front monitor byrefraction. The grating grooves may be of course replaced by the surfaceof a lens.

In the first through sixth embodiments, the region of the front monitorlight-guiding plate through which the light beam is guided to the frontmonitor by refraction is assumed to be a flat surface. The region may ofcourse is curved.

Alternatively, the front monitor light-guiding plate may be formed of abowl-shaped lens, and the refractive index of the front monitorlight-guiding plate may be set freely.

The optical pick-up device according to the first through sixthembodiments of the present invention is compact in size and can bemanufactured at low cost. Then, through the use of the optical pick-updevice, the sufficient amount of light can be led to the front monitor,and the amount of light irradiated onto the optical disc can bemonitored with accuracy, without being affected by the stray light.

While we have shown and described several embodiments in accordance withour invention, it should be understood that disclosed embodiments aresusceptible of changes and modifications without departing from thescope of the invention. Therefore, we do not intend to be bound by thedetails shown and described herein but intend to cover all such changesand modifications within the ambit of the appended claims.

1. An optical pick-up device comprising: a laser diode; an objectivelens focusing a light beam emitted from the laser diode on an opticaldisc; an optical detector receiving a light beam reflected from theoptical disc; a beam splitter passing the light beam emitted from thelaser diode and the reflected beam therethrough or reflecting the lightbeam emitted from the laser diode and the reflected beam; a frontmonitor receiving the light beam emitted from the laser diode; and afront monitor light-guiding plate guiding a part of the light beamemitted from the laser diode to the front monitor; wherein the frontmonitor light-guiding plate is arranged between the laser diode and theobjective lens; and wherein a region of the front monitor light-guidingplate illuminated by the light beam emitted from the laser diodeincludes a first region having a predetermined shape for causing thepart of the light beam emitted from the laser diode to change atraveling direction thereof by refraction and then reach the frontmonitor.
 2. The optical pick-up device according to claim 1, wherein thefirst region of the front monitor light-guiding plate is illuminated bythe part of the light beam outside an effective diameter of theobjective lens.
 3. The optical pick-up device according to claim 2,wherein the first region of the front monitor light-guiding platecrosses a straight line passing through a center of the part of thelight beam to be irradiated onto the front monitor and perpendicular toan active layer in a laser chip of the laser diode.
 4. An opticalpick-up device comprising: a laser diode; an objective lens focusing alight beam emitted from the laser diode on an optical disc; an opticaldetector receiving a light beam reflected from the optical disk; a beamsplitter passing the light beam emitted from the laser diode and thereflected beam therethrough or reflecting the light beam emitted fromthe laser diode and the reflected beam; a front monitor receiving thelight beam emitted from the laser diode; and a front monitorlight-guiding plate guiding a part of the light beam emitted from thelaser diode to the front monitor; wherein the front monitorlight-guiding plate is arranged between the laser diode and theobjective lens; wherein a region of the front monitor light-guidingplate illuminated by the light beam emitted from the laser diode has afirst region and a second region, the second region being a part of theregion different from the first region; and wherein each of the firstregion and the second region has a predetermined shape for causing thepart of the light beam to change a traveling direction thereof byrefraction and then reach the front monitor.
 5. The optical pick-updevice according to claim 4, wherein each of the first region and thesecond region is illuminated by the part of the light beam outside aneffective diameter of the objective lens.
 6. The optical pick-up deviceaccording to claim 5, wherein each of the first region and the secondregion of the front monitor light-guiding plate crosses a straight linepassing through a center of the part of the light beam to be irradiatedonto the front monitor and perpendicular to an active layer in a laserchip of the laser diode.
 7. The optical pick-up device according toclaim 6, wherein the first region in the front monitor light-guidingplate is arranged opposite to the second region with respect to a linepassing through the center of the part of the light beam to beirradiated onto the front monitor and parallel to the active layer inthe laser chip of the laser diode.
 8. The optical pick-up deviceaccording to claim 1, wherein grating grooves are formed in the regionof the front monitor light-guiding plate different from the first regionhaving the predetermined shape.
 9. The optical pick-up device accordingto claim 1, wherein the region of the front monitor light-guiding platedifferent from the first region having the predetermined shape iscurved.
 10. The optical pick-up device according to claim 4, whereingrating grooves are formed in the region of the front monitorlight-guiding plate different from the first and second regions.
 11. Theoptical pick-up device according to claim 4, wherein the region of thefront monitor light-guiding plate different from the first and secondregions is curved.
 12. The optical pick-up device according to claim 8,wherein the front monitor is arranged in a position being more aheadthan the beam splitter in the traveling direction of the light beamemitted from the laser diode.
 13. An optical recording disc systemincluding the optical pick-up device according to claim 1 and a laserdiode control circuit for controlling an amount of light emitted fromthe laser diode by using a signal output from the front monitor of theoptical pickup device.